The present invention relates to a drive system for a metal extrusion press and, more particularly, for the return movement of the container holder and the travelling beam of a metal extrusion press.
A metal extrusion press can have a travelling beam provided with a ram which is juxtaposed with a counter beam which can support an extrusion die through which the metal of a billet held in a container on a container holder between the travelling beam and the counter beam is extended.
A cylinder beam can be provided with a main cylinder unit acting upon the travelling beam for driving the ram into the billet and the metal through the die and with auxiliary cylinder units for the travelling beam and the container holder.
The annular compartments of the auxiliary cylinders for the container holder can be pressurized for the return movement and the full-piston-area cylinder compartments can be connected with a tank. The auxiliary cylinder units for the container holder are thus able, in a first control phase to maintain a mechanical contact of the container holder against the travelling beam and then to shift the travelling beam via the container holder into a billet loading position.
For hydraulic extrusion presses it is important to minimize the time required to relieve the press, remove the billet residue from the container holder, load a new billet into the container holder and commence the pressing operation once again. The minimization of this time period results in an increase in productivity.
To achieve such a minimization in the return and refilling time, the velocity of the container holder and the travelling beam during their return or inactive strokes must be increased.
The pump capacity of the high pressure pump used for extrusion usually does not suffice for such high speed return strokes. It is possible to obtain the rapid movement by the use of additional high pressure pumps, auxiliary pumps or special means like additional accumulators or similar systems for augmenting the volume rate of flow of the hydraulic fluid.
It is, however, a drawback of such systems that they involve high investment or capital costs and additional electronic power and often require the installation of special units for effecting the inactive return displacement of the parts.
After extrusion, the extrusion press must have its elements moved away from one another to provide sufficient place for removing the container residue and introducing the new billet. In a first phase, the conductor or conductor holder and then travelling beam must be moved rearwardly parallel to one another. This is usually achieved with the cylinder units in a manner such that the container and the travelling beam is separately displaced or the container holder is brought into engagement with the travelling beam and then entrains the travelling beam with it. The moving parts are thus simultaneously or sequentially brought into the billet loading position. With the prior art cylinder arrangement of the extrusion press, differential switching is required to reduce the hydraulic volumetric displacement. This differential switching is also referred to as regenerative switching or as hydraulic pressure takeover.
In conventional practice this is used to accelerate the press closing or forward operation stage but not for a rapid return or separation operation.
It is, therefore, an object of the invention to provide an improved metal extrusion press with a drive system which enables accelerated return movement of the container holder and the travelling beam entrained thereby significantly reducing the setup time for the next extrusion operation.
Another object of the invention is to provide a system for effecting such acceleration which does not require additional apparatus like further pumps or accumulators.
These objects and others which will become apparent hereinafter are attained, in accordance with the invention, in a metal extrusion press which comprises:
a traveling beam provided with a ram;
a counter beam supporting an extrusion die juxtaposed with the ram;
a container holder between the press beam and the counter beam and provided with a container receiver a billet of a metal to be extruded between the ram and the die;
a cylinder beam provided with a main cylinder unit comprised of at least one piston-and-cylinder assembly acting upon the traveling beam for driving the ram into the billet and the metal through the die, and with traveling-beam and container-holder auxiliary cylinder units each consisting of at least two piston-and-cylinder assemblies and respectively braced between the cylinder beam and, respectively, the traveling beam and the cylinder holder; and
a hydraulic system connected to at least some of the piston-and-cylinder assemblies for a return stroke of the container holder and traveling beam, the piston-and-cylinder assemblies of the auxiliary cylinder units each having an annular cylinder chamber traversed by piston rods on one side of the respective assembly and a full-piston-area cylinder chamber on an opposite side of the respective assembly, the system pressurizing the annular cylinder chambers and connecting the full-piston-area cylinder chambers of the piston-and-cylinder assemblies of the auxiliary cylinder unit of the container holder to a tank. The auxiliary cylinder unit of the container holder maintains the container holder in mechanical entrainment with the traveling beam in a first phase and the traveling beam is thereafter pushed into an end position by the container holder, the system including means for connecting the annular cylinder chambers of the auxiliary cylinder units of the container holder and the traveling beam and the full-piston-area of the travelling beam to a hydraulic pressurization source simultaneously during the return stroke.
More particularly, during the back movement of the container holder, the ring chambers of the container auxiliary cylinders are connected to the hydraulic pressure source and the cylinder chambers on the opposite sides of the respective pistons, here referred to as the full piston area chambers, are connected to the tank via the valve unit. After the container holder comes into contact with the travelling beam, and after a short acceleration phase via the valve unit, the ring chambers auxiliary cylinder units of the travelling beam are connected with the full piston area cylinder units of the travelling beam auxiliary cylinder units in a hydraulic short circuit and simultaneously the valve unit returns the surplus hydraulic fluid generated by the mechanical entrainment of the travelling beam to the ring chambers of the auxiliary cylinder units of the container holder. The cylinder areas of the auxiliary units are so selected that the requisite force is maintained for the return movement of the container holder and the travelling beam.
The differential hydraulic switching which results from the foregoing insures that in the return stroke, the auxiliary cylinders for the container holder and the travelling beam will work together in the return movement and that the hydraulic fluid quantity which, in earlier systems, was simply discharged into the tank from the full piston area side of the auxiliary units of the travelling beam, can be fed to the ring chambers of the travelling beam and the container holder auxiliary cylinders to accelerate the return movement. As a consequence, for a given installed pump capacity as required for the press operation, the return speed can be increased and the recycling time shortened. The hydraulic fluid discharged from the full piston area cylinder chambers of the auxiliary cylinder units of the travelling beam, limited only by the hydraulic fluid requirements of the ring chambers of the auxiliary units, is returned by the pressurization unit to both the auxiliary cylinder units of the container holder and the travelling beam.